Cool bean

Hi everyone, thanks for all the wisdom shared on this site; it's guided me well during the restoration of my 74 coupe!

I'm planning on a top end build to eek out as much power as possible from original L48. First, a word on my application: I want a cruiser with plenty of punch. I won't be building for the track, but may do a run two to check out what it can do. :-) I'm not concerned about keeping perfectly stock. I don't know if the motor has been rebuilt. The compression test results are all 140/145 psi per cylinder.
budget: $1500 range for parts; I will do the install.

What's already on the motor (and i plan on using after the top-end build):

• Holley 600, vac secondaries, electric choke.
• Holley Contender intake
• Stock distributor, Pertronix Ignitor III, Flamethrower coil.

A built 7004r is replacing the THM-400 and I'm keeping the stock 3.08 rear. (Most of the miles put on this cruiser will be highway, with spirited driving now and then.) I plan on using a 2000 stall converter.

Here's the shopping list for the build. How can I estimate HP & TQ at the crank? I'm hoping to top 400HP/400 TQ. Should I consider anything else? Are these the best choices given application/budget?

• COMP Cams XE262H cam (262/270 advance duration, 218/224 duration at .050, .462/.469 valve lift, 110 lobe separation) OR Comp Cams CCA-CL12-238-2
• Comp Cams 1.6:1 Magnum roller tip rockers PN 1418-1
• GM Vortec iron heads SDPC PN SD8060A (64cc chambers, 170cc intake runner volume, 1.94/1.50 valves OR Edlebrock EDL-5089
• Long tube headers, 2 1/2 exhaust. (is there a performance difference between "shorty" and "long tube"?

augiedoggy

for $1,500 I was able to scour craigslist and ebay and buy a machined block and build my entire engine using a lunati voodoo 262 cam with matching srprings and lifters which performed much better in dyno 2000 than the comp version without giving up any lower end power with the dart 64cc /180 iron eagle heads and flat top pistons... I bought a scat crank and an avenger 670 carb with a polished professional products rpm clone intake and a 3 row champion rad. I too used 1.6 roller rockers (harland sharp) and for $850 more I added obx stainless header/sidepipes with 2 1/4 sweet thunder baffles... the 74 turbo 400 trans has a 2000 rpm stall from the factory but I would like to do a 200r4 swap myself since Ive read its a much better swap for ours cars over the longer 700r4

my engine specs out (according to the optimistic dyno2000 program) to have 396hp and 414lbs of toque so your not too far off with the dished pistons being the biggest obstacle to power for you.

softwarejanitor

Aluminum heads are worth around 30lbs weight savings. General rule of thumb says every 100lbs of weight savings is generally worth about a tenth of a second in the 1/2 mile. And weight savings from the front of a nose heavy car like a C3 result in handling improvements too. There are a few other parts you can swap out to save weight... aluminum water pump, etc.

Yes, shorty headers will generally only get you 10-15 HP increase over the cast iron ram's head exhaust manifolds normally found on a smog motor like an L48, long tube headers will get you more like 20-25 HP. In order to get those increases you also need at minimum a high flow catalytic converter if not a higher performance cat-back system. You can get a bit more than those figures if you put in a true dual exhaust system.

FWIW, the intake, cam, heads & exhaust mods you list on your L48 should get you from the 180 HP stock range to around 250 HP or so. That's enough to feel, but the TH700R4 will be more noticeable as it has a much lower low gear to launch better (especially if you combine it with a 2000 stall converter) and on the highway the overdrive 4th will make it cruise a lot smoother and get much better mileage.

To get to 400 HP you will need to be a lot more aggressive than those mods. Maybe nitrous. You probably might also want to consider putting in splayed steel 4 bolt mains into your factory 2 bolt block if you get into the 400 HP range, maybe even a steel stroker crank. Your 2 bolt L48 block and nodular iron crank probably fine up to 300 to 350 HP though. Also a 600 cfm carb might not be enough for a 400 HP engine. Might want to go with a 700 cfm or even a 750 cfm.

Edit -- 1974? What am I thinking... Ignore what I said about catalytic converter... You shouldn't have one... and you should have dual exhaust already...

softwarejanitor

Not to be a dream crusher but that sounds extremely optimistic. Realistically I'd be surprised to see either of those parts combinations break 300 HP and 325 ft/lbs of torque.

toobroketoretire

I fully agree with you as his proposed combination will barely make 300 horsepower. For an honest 400 horsepower he'll need an 11 to 1 compression ratio, 2.02" X 1.60" heads, and a camshaft with at least 245 degrees of duration with 106 to 108 degree lobe centers. And then the gain will come at the higher rpm range like 5000 to 6000 rpm where street engines rarely operate very long. For a BIG performance gain change over to a set of 3.73 gears with the TH700R4 and it'll gain a LOT of performance for little dollars.

Shark Racer

I think the engine will make 325-350 hp, definitely over 325. Those heads flow better than pretty much any out of the box factory small block offering that came in a Corvette and the cam is decent too, then he added headers on top of it.

However, one thing worth noting is that the intake manifold you have right now will not work with Vortec heads - you'll need to get a vortec intake.

augiedoggy

cast cranks are realistically fine on engines up to 500hp that dont regularly see anything north of 6000rpm from everything Ive been reading.

augiedoggy

I know its not likely as high as the program says but its certainly more than 300hp... you must have a crystal ball because you dont even know what my compression ratio or quench is...?

I had year to research my combination and search online for others with similiar setups and there were a number of people with almost identically flowing heads and the same pistons/cam with high compression and a small quench who were seeing around 370hp and over 400lbs or torque on the dyno... and I actually found a magazine article with an almost identacal setup to mine only with different heads and it pulled some impressive numbers...
I must have put at least 20 different cam choices through the math software before I settled on the cam I did because it worked best with the flow characteristics of the heads I had and I could still run pump gas without worries (93) although so far ethanol free 91 has been ping free too.

the only way I'll know for sure is to have it dynoed but right now thats the least of my concerns.

(and I did use a 4 bolt block myself for the reasons stated already... the original block is sitting on the engine stand in my garage.)

augiedoggy

I think your talking about the OP and the guy you quoted is talking about my setup...
I do have 2.02 x 1.60 valve heads btw with 180cc runners and 64cc chambers. my heads are old but they have fairly close flow numbers to vortec heads if I remember right.

the biggest realistic power limiting difference between the OPs proposed setup and mine is the L48's low compression dished pistons right? although I do have to admit I did notice more power when going from my 600cfm elelbrock carb to the avenger 670 carb after rejetting despite what the math says there..

OMF

I think your going to be shy of your power goals with the chosen parts. The biggest obsticle is your cam choice. If you step it up to the next one (xe268H) with the 1.6 rollers (.508/ .512 lift) and good flowing vortec heads along with a performer RPM VORTEC intake you'll be very close in my opinion. Use the steel shim head gasket with the 64cc head chambers will bump compression up to about 9.5/1.....all working in your favor.
A small amount of pocket porting in the bowl area, just blending and smoothing.....not removing much metal will also help....watch a few videos to get an idea whats required.

bluedawg

I suggest a 2400 rpm stall with either 262 cams.

REELAV8R

I'm not sure what the flow numbers on a 170 cc runner vortech head are. A 170 cc intake runner is for lower rpm torque vs high rpm power.
The cam you are using is also built for smooth idle and low rpm torque.
The valve lift on the vortech is limiting unless modded appropriately for greater lift so not sure if the 1.6 R rockers are going to work without that mod.
The limiting factor on you parts looks to be cylinder filling above 4500 rpm or so. This will limit the HP potential as RPMs increase.
A roller cam and more lift ( .50 or more) and better flowing heads will put you in the 400 hp range. Think AFR heads.
My combo has a 219@.050 intake and exhaust on a roller cam with ported dart SHP heads with 195 cc runners 2.02/1.6 valves, side pipes with hooker headers and tops out around 5200 rpm in power. Got 377 ish gross at the crank.
The cam rocker combo has .549 valve lift on a 108 LSA. 108 vs 110 is worth maybe 20 hp. Running a 2600 stall converter with a TH-350 to a 308 rear end.
Roller cam with that duration on a 195 cc runner AFR head and you'll be in the 400 hp area I would guess.

augiedoggy

REELAV8R actually helped me crunch numbers with my build...

In case the op is interested in the specs on the voodoo 262 cam (which has more lift and duration than the comp cam) and the general power curve, I attached the dyno2000 sheets for my build... again the numbers are optimistic but I do believe 350hp is very realistic and theres plenty of torque for the 3.08 gears in my 74

I want to say the sheets below had an error in them and once it was corrected my power numbers actually went up a bit more but I cant find the later digital file for some reason.

dochorsepower

I hate to rain on the horsepower parade here but what about the condition of your existing L48 lower end? I agree that the heads and cam of the L48 are the worst part of the package but are you just putting a new saddle on an old horse? Maybe you would be better served waiting to do a complete engine package.

Cool bean

Thank you for all your replies; there's fantastic knowledge and sage advice here. I've adjusted my L48 top end list and approach (below) along with a brief reason why.

For back ground: I started this research using keywords like "400 hp sbc budget build" and similar terms. The goal: cruiser, pump gas, max hp/tq and rpms that the L48 bottom end can handle. The initial shopping list was the result of conversations with Summit and also the Danger Mouse series of articles in SuperChevy. In Danger Mouse Recap Part 15, they acknowledge the "Best Build" in terms of bang-for-the-buck is Danger Mouse Part 6. (Vortex heads, XE262 Cam, Speed Demon carb, RPM intake). That's the list I'm using as a guide; I can't/won't match it exactly. (they have a .030-over short block with lunati rotating assembly which isn't happening for me in this round.)

• Exhaust: Long tube headers (thank you @softwarejanitor). Ceramic coated. Stainless 2 1/2 dual exhaust. Flowmaster mufflers.
• Bottom end: clean up, inspect, gaskets/seals, and paint when I pull it. Maybe the splays. However, budget won't permit a build this year or next, hence the top-end only decision. @dochorsepower, you're right, but I'm taking a calculated risk on how long my existing bottom end can last.
• Heads: I like the weight savings aluminum offers, thank you again @softwarejanitor! @REELAV8R, Good point of valve lift and extra machining; hopefully aluminum heads will help avoid this extra work. (I'm thinking something from AFR, Edlebrock, etc)
• Rockers: 1.6 rollers.
• Cam: change to more aggressive. @SStocker31, I get what you're saying about the XE268H. I like a stock idle but well...this is going to be a compromise cruiser-idle versus power. We'll see where it lands.
• Intake: yep, I missed that @SharkRacer, 'can't use my Holley contender with a head change. Edlebrock RPM it is.
• Carb: Same goes for my Holley 600. The DangerMouse article specified a SpeedDemon 750. I might start out with my Holley and upgrade later. Other research shows the incremental difference in carbs is measurable, but not worlds apart. This will be a wait-and-see item. I'm going to take from the 'carb budget" and apply it to the new manifold.

@Augiedoggie, I couldn't agree more about scavenging in the second-hand market. Even though it can be dicey, there's good deals to be had, but only with research. Internal engine parts are tricky. I'm also going try my luck in August at Carlisle; it's a manageable day trip from S. NJ.

augiedoggy

I read that same danger mouse article when building my engine... and my 30 over flat top block is pretty damn close the the setup they used if I remember correctly.

REELAV8R

I believe Vizards claims that 2 bolt main is good for 450 hp. I'm running two bolt with no worries.
The stock pistons are cast aluminum. Have about a 350 hp limit IIRC. Hypertectic flat tops or d- dish tops is a far better option.
Quench can be a major limitation to power production. The stock Pistons have no quench area due to the piston top design. That in itself will limit you CR, thereby your cam choices, and the cylinder pressure you can develop without detonation.
Detonation is the limiting factor for cylinder pressure on a gas engine for a given octane. Many factors are involved in avoiding detonation but quench is a large one. Quench induces combustion chamber turbulence which gives a more homogenous mixture reducing hot spots and spontaneous, and unwanted combustion independent of spark ignition. Remember torque is what gets the car moving. The more you can develop without detonation the better.
Your 700r4 will help in this area as it reduce your gear ratio in first gear, but you could encounter issues in subsequent gears, I'm thinking third or fourth gear at large throttle openings.
A higher stall will also help as it gets the RPMs higer reducing effort required by the engine in the lower, detonation prone, RPMs.

softwarejanitor

They are more optimistic than I am... I'd not want to go past 400 HP with 3 bolt mains. The splayed steel caps you can buy are reasonably priced enough and easy enough to install that I'd think them nearly a no-brainer if you were building a high output engine and you had a 2 bolt factory block. The splayed steel caps are way stronger than a nodular iron 4 original cap.

350 HP with 2 bolts not likely a problem, something else will probably break first but I wouldn't feel real good about using cast pistons past 300 HP personally...

Absolutely agree, and they are not nearly the bank breakers that forged pistons are.

A good point. One place where you do often want to use dish top pistons is with a supercharged engine... But then of course you don't worry so much about swirl.

Also aluminum gives a much better heat disbursement for cylinder heads which is part of why they can usually handle a little more compression than cast iron heads.

I agree with all of those points.